Buggy code:
final class RS232Packet implements IPacket { private final List < Byte > data = new ArrayList < > ( ) ; private final EnumSet < Events > event = EnumSet . of ( Idling ) ; private CreditActions creditAction = NONE ; private String message = "" ; private BillNames billName ; RS232Packet ( ) { } RS232Packet ( byte [ ] bytes ) { } @ Override public boolean isValid ( ) { } @ Override public String getByteString ( ) { } @ Override public byte [ ] toBytes ( ) { } @ Override public int size ( ) { } @ Override public byte get ( int index ) { } @ Override public IPacket pack ( ) { } @ Override public boolean replace ( int index , byte b ) { } @ Override public boolean or ( int index , byte b ) { } @ Override public IPacket parseAsNew ( byte [ ] bytes ) { for ( byte b : bytes ) this . data . add ( b ) ; RS232Configuration config = RS232Configuration . INSTANCE ; if ( ( sum ( data ) ) == 0 ) { message = "Acceptor<seq2seq4repair_space>Bus//Not<seq2seq4repair_space>Connected" ; } else <START_BUG> if ( ( ( data . size ( ) ) == 11 ) || ( isValid ( ) ) ) { <END_BUG> config . toggleAck ( ) ; byte t3 = data . get ( 3 ) ; if ( ( t3 & 1 ) == 1 ) event . add ( Idling ) ; else if ( ( t3 & 2 ) == 2 ) event . add ( Accepting ) ; else if ( ( t3 & 4 ) == 4 ) event . add ( Escrowed ) ; else if ( ( t3 & 8 ) == 8 ) event . add ( Stacking ) ; else if ( ( t3 & 32 ) == 32 ) event . add ( Returning ) ; if ( ( t3 & 16 ) == 16 ) { event . add ( Idling ) ; event . add ( Stacked ) ; } if ( ( t3 & 64 ) == 64 ) { event . add ( Idling ) ; event . add ( Returned ) ; } byte t4 = data . get ( 4 ) ; if ( ( t4 & 1 ) == 1 ) event . add ( Cheated ) ; if ( ( t4 & 2 ) == 2 ) event . add ( BillRejected ) ; if ( ( t4 & 4 ) == 4 ) event . add ( BillJammed ) ; if ( ( t4 & 8 ) == 8 ) event . add ( StackerFull ) ; if ( ( t4 & 16 ) == 0 ) event . add ( BillCasetteRemoved ) ; byte t5 = data . get ( 5 ) ; if ( ( t5 & 1 ) == 1 ) event . add ( PowerUp ) ; if ( ( t5 & 2 ) == 2 ) event . add ( InvalidCommand ) ; if ( ( t5 & 4 ) == 4 ) event . add ( Failure ) ; byte credit = ( ( byte ) ( ( t5 & 56 ) > > 3 ) ) ; if ( ( credit != 0 ) && ( event . contains ( Escrowed ) ) ) { if ( ( credit & ( config . getEnableMask ( ) ) ) == credit ) creditAction = ACCEPT ; else creditAction = RETURN ; } if ( event . contains ( Stacked ) ) { event . add ( Credit ) ; billName = BillNames . fromByte ( credit ) ; Logger . getLogger ( RS232Packet . class . getName ( ) ) . log ( Level . INFO , String . format ( "Crediting<seq2seq4repair_space>%s" , billName . toString ( ) ) ) ; } } else { if ( data . isEmpty ( ) ) message = "No<seq2seq4repair_space>Response" ; else if ( ( data . size ( ) ) != 11 ) message = "Bad<seq2seq4repair_space>Message<seq2seq4repair_space>Length" ; else message = "Bad<seq2seq4repair_space>checksum" ; } return this ; } @ Override public EnumSet < Events > getInterrpretedEvents ( ) { } @ Override public String getMessage ( ) { } @ Override public String toString ( ) { } @ Override public boolean equals ( Object object ) { } @ Override public int hashCode ( ) { } @ Override public CreditActions getCreditAction ( ) { } @ Override public BillNames getBillName ( ) { } private int sum ( List < Byte > d ) { } private String byteListToString ( List < Byte > l ) { } }

Fix:
if ( ( ( data . size ( ) ) == 11 ) && ( isValid ( ) ) ) {